Brayton cycle engines generally comprise means for compressing air for the support of combustion, a combustion chamber which has inlets for both the compressed air and fuel, and means for extracting energy from the hot exhaust gases to produce mechanical work. When a turbine is used to extract energy, the hot exhaust gases produced in the combustion chamber are fed to a turbine that rotates a drive shaft. In a recuperated turbine engine, exhaust gases of the turbine are passed through a recuperative heat exchanger that heats the relatively cold compressed air from the compressor to maximize efficiency of the engine.
The efficiency of the recuperated gas turbine engine depends in part on the efficiency of the heat exchanger. The heat exchanger utilizes residual energy contained in the hot exhaust gases for preheating the compressed air supplied to the turbine. The efficiency of the heat exchanger is the ratio of heat actually transferred in the heat exchanger to the heat theoretically transferable by an infinitely large heat exchange surface. Because of the high temperature on the hot gas side of the heat exchanger, the materials used must be limited to highly heat resistant metals or ceramic materials. A critical factor is that leakage between the hot exhaust and cold high pressure air sides of the heat exchanger must be precluded.